This invention relates to piezoelectric oxide materials, particularly, to those having a binary metal oxide system of PbTiO.sub.3 -Pb(Co.sub.1/2 W.sub.1/2)O.sub.3 in which Pb is partly replaced by at least one element selected from the group consisting of Ba, Sr and Ca.
As is well known, piezoelectric materials are used in wide fields including ultrasonic vibration elements, transducer elements of, for example, mechanical filters, elements of ceramic filters and ceramic vibrators, and elements of vibrometers and accelerometers. Various efforts are being made to provide improved piezoelectric materials based on a binary metal oxide system of PbTiO.sub.3 -PbZrO.sub.3 for use in such fields. For example, it has been proposed to mix additives such as Bi.sub.2 O.sub.3, Cr.sub.2 O.sub.3, MnO.sub.2 and ZnO into a binary system of PbTiO.sub.3 -PbZrO.sub.3 in order to provide materials having an improved piezoelectric property. Further, piezoelectric materials based on a ternary system of PbTiO.sub.3 -PbZrO.sub.3 -(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 are also under development. However, these piezoelectric materials have a curie point of about 300.degree. C. and, thus, can not be used under temperatures higher than 300.degree. C. Also, these piezoelectric materials have a dielectric constant as large as about 1,000 and, thus, are unsuitable for use in a high frequency region.
Also reported are PbTiO.sub.3 type piezoelectric materials having a dielectric constant as small as 150 to 250. However, these materials tend to bear cracks after subjected to a sintering treatment, rendering it impossible to prepare a large sintered mass having a diameter of 20 mm or more. Naturally, the PbTiO.sub.3 type material is unsuitable for use as a piezoelectric material generating a strong ultrasonic wave and for forming transducing elements of probes for linear scan type ultrasonic diagnosis apparatus. An additional difficulty inherent in the PbTiO.sub.3 type material is a severe polarizing condition. Specifically, it is necessary to apply an electric field of as high as 60 KV/cm at 200.degree. C. in order to polarize the PbTiO.sub.3 type piezoelectric material, leading to a low yield of the product. Further, the conventional PbTiO.sub.3 type material has a mechanical quality factor Qm of about 1,000 at most.